making a limb Flashcards
what are sites of limb outgrowth and what dtermines where these form?
limb buds - hox genes
what happnes in homozygous HOXB5 knockout mice?
their legs / forelimbs form at a more anterior level
is FGF sugnalling required/sufficient for limb bud formation?
is both sufficient and required
what are 3 zones of the limb bud?
apical ectodermal ridge
progress zone
zone of polarisng activity
what would removal of AER result in?
truncation of limb
FGF4 bead can substitute for aer
what is AER?
ridge of thickened epithelium around tip of limb bud
what does AER maintain?
progress zone (signals to maintain cell division )
what is progress zone?
distal region of limb bud mesenchyme containing undifferentiated dividing cells
how does PZ relate to cell fate?
length of time cell spends in PZ determines its cell fate along P-D axis
what is ZPA?
posterior mesenchyme that acts as an organising centre to pattern AP axis of limb
what happens when zpa is transplanted underneath AER?
induced symmetrical duplications or normal limb bud elements
where is SHH expressed?
in ZPA by cells responding to ZPA - causes gradient of Shh
what genes are expressed in overla[ping zones of limb bud?
HOxa and HOx d
what happens in hox a and hoxd are delted?
loss of shh expression and limb truncation
how are digits formed?
programmed cell death
differential gowth in amphibians
